A difference comparator is a circuit that accepts inputs and determines a difference between them. Typical difference comparators take two inputs and return a signal indicating which of the signals is higher. Many circuits use difference comparators, such as analog to digital converters (ADC) or transceiver circuits.
Difference comparators are commonly used in communications systems to communicate signals between different circuits. For noise-immunity reasons, most communication standards utilize differential signaling. In differential signaling, data is transmitted in the form of a differential voltage across two nodes.
An ideal difference comparator amplifies only the voltage difference between two inputs. Voltages common to both inputs are ideally rejected. However, due to differing communication standards the common mode voltage utilized by various transmitters can vary widely between different transmitters. For example, some standards pick a high common mode voltage ranging, for example, between 700 mV and 1300 mV. Some standards, on the other hand, pick a low common mode voltage ranging, for example, between 145 mV and 350 mV. Transceiver circuits operating according to other standards output common mode voltages between 500 mV and 700 mV when operating in AC-coupled environments. In order to accommodate these various differential transmission circuits, a flexible receiver design needs to be able to accept any common mode voltage between the ground (0 mV) and the termination voltage (about 1200 mV).
One or more embodiments of the present invention may address one or more of the above issues.